1. Field of the Invention
The present invention relates to an image search device for allowing the observer to look at any desired area of an image formed through an objective optical system.
2. Description of the Related Art
An endoscopic apparatus of a certain type designed for medical applications is installed with an image search device that displays an enlarged view of a part of a wide angle image of an object formed through an objective optical system arranged at a distal end of the endoscope and allows the observer to search a target area to be observed within the wide angle image by shifting the enlarged view within the wide angle image.
Known endoscopic apparatus are so designed that the image pickup device is shifted in the enlarged image formed through the enlarging optical system vertically and horizontally or that the image formed through the objective optical system is shifted vertically and horizontally in the visual field of the enlarging optical system, so that the observer can search the target area to be enlarged and observed in the image formed through the objective optical system.
However, the endoscopic apparatus in which the image pickup device having a smaller image pickup area than the enlarged image formed through the enlarged optical system is shifted vertically and horizontally is inevitably made to have large dimensions, because the image pickup device needs a relatively large space where it can move inside the apparatus. On the other hand, with the endoscopic apparatus in which the image formed through the objective optical system is shifted by deflecting the object light coming from the objective optical system by means of a variable angle prism, decentering aberration occurs to the enlarged image, because of the relative decentering of the surfaces of the variable angle prism. Additionally, with the endoscopic apparatus in which the image formed through the objective optical system is shifted by rotating a pair of planar mirrors, the image plane formed through the objective optical system is inclined relative to a plane perpendicular to the optical axis of the enlarging optical system and the obtained image is rotated in the image plane.
One object of the present invention is to provide an image search device in which image formed through its objective optical system can be shifted relative to the visual field of its image re-forming optical system, in order to allow the observer to look at any desired area of the image formed through the objective optical system, in a plane perpendicular to the optical axis of the image re-forming optical system without producing any decentering aberration, inclination nor rotation of the image.
In present invention, the above object is achieved by providing an image search device with an objective optical system which forms an image of an object, an image erecting optical system having at least four reflection planes, a first image re-forming optical system to which object light having passed through the objective optical system and the image erecting optical system enters and which re-forms the image from the object light, and a drive mechanism which moves the image erecting optical system in a direction perpendicular to the optical axis of the objective optical system.
With this arrangement, as the image erecting optical system is moved by the drive mechanism, the position where the image is formed through the objective optical system is relatively shifted with the optical axis of the first image re-forming optical system in a direction perpendicular to the optical axis, while the image plane of the objective optical system is maintained to be perpendicular to the optical axis of the first image re-forming optical system. As a result, the image re-formed through the first image re-forming optical system does not carry any decentering aberration, inclination relative to a direction perpendicular to the optical axis of the first image re-forming optical system, nor rotation about the optical axis. xe2x80x9cAn image erecting optical systemxe2x80x9d means in this specification an optical system which inverts and reverse an image formed through the objective optical system or a relay optical system before the image erecting optical system itself. It is not necessary that the image formed after passing through the image erecting system has the same orientation as the object.
An image search device according to the invention may be incorporated into a rigid endoscope or a fiber scope or into a monitor camera.
The drive mechanism which moves the image erecting optical system may be manually operated or electrically powered.
The image erecting optical system of the image search device according to the invention may be a Pechan prism having a roof, an Abbe prism having a roof, a first type Porro prism, a second type Porro prism, a plurality of mirrors arranged at positions equivalent to the reflection planes of any one of such prisms or some other image erecting optical system having four or more reflection planes. In any case, the image formed through the objective optical system is relatively shifted within the image plane as the image erecting optical system is moved in a direction perpendicular to the optical axis of the objective optical system.
The image search device according to the invention may have a structure where the image formed through the objective optical system is re-formed only through the first image re-forming optical system, or a structure where object light coming from the objective optical system is separated into a light path passing through the first image re-forming optical system to re-form the image and into other light path passing through a second image re-forming optical system to re-form the image covering a different field of view than the image formed by the first image re-forming optical system. In case the image is re-formed only through the first image re-forming optical system, the image search device may additionally has an image pickup device which picks up the image formed through the first image re-forming optical system. On the other hand, in case the image is re-formed independently through the first and second image re-forming optical systems, the image search device may additionally has a first image pickup device which picks up the image formed through the first image re-forming optical system and a second image pickup device which picks up the image formed through the second image re-forming optical system.
A half mirror may be used to separate the object light coming from the objective optical system. If the image erecting optical system is formed by four reflection surfaces arranged at positions equivalent to those of a Porro prism, foremost one of the reflection planes may be made as the half mirror through which the object light passing through the reflection surface of the half mirror enters the second image re-forming optical system.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-346439 (filed on Nov. 14, 2000), which is expressly incorporated herein by reference in its entirety.